1. Field of the Invention
The present invention relates to a lens driving apparatus for a disc player which records information on a disc and/or reads the recorded information from the disc. In particular, the present invention relates to the structure of a lens driving apparatus using a flat coil.
2. Description of Related Art
There is known a lens driving apparatus which drives an objective lens in an optical axis direction of the lens (i.e., focus direction) for converging a reading beam onto the disc surface, at the time of reading the information from a disc on which information is optically recorded, and drives the objective lens in the direction perpendicular to the optical axis of the lens (i.e., tracking direction) to enable the reading beam to follow the information track.
The Japanese Patent Application Laid-Open under (JP-A) No. 2001-229557 discloses an example of such a lens driving apparatus. The lens driving apparatus is of a print coil type, which includes flat coil substrates formed by patterning and etching a focus coil and tracking coils, fixed on the both side surfaces of a holder holding an objective lens by an adhesive or the like. In this kind of the lens driving apparatus, in order to arrange the focus coil and the tracking coils at appropriate positions with respect to the magnetization boundary line of a magnet magnetized substantially in a U shape, the focus coil and the tracking coils need to be formed displaced with each other on the coil substrate. In the above-mentioned example of the lens driving apparatus, the focus coil is disposed at a position above the tracking coil in the optical axis direction of the lens. Therefore, the coil substrate needs to have a certain length in the optical axis direction of the lens, and hence there is such a problem that the lens driving apparatus becomes large in size.
In contrast, the Japanese Patent Application Laid-Open under (JP-A) No. 2001-118265 discloses a lens driving apparatus of other type. In this lens driving apparatus, a coil functioning as both a focus coil and a tracking coil is formed on a coil substrate so that the width of the coil substrate in the up and down direction (i.e., the optical axis direction of the lens) is made smaller.
However, in this lens driving apparatus, since the coil serving as both the focus coil and the tracking coil is used, the polarity of the electric current supplied to the coil should be switched for the focus control and the tracking control, and there is such a problem that the control is complicated.
The present invention is achieved in order to solve the above problems. It is an object of this invention to provide a coil substrate for a lens driving apparatus capable of achieving miniaturization without the need of complicated control, such as the switching control of the current supply to the coil.
According to one aspect of the present invention, there is provided a coil substrate for a lens driving apparatus including: a substrate of substantially rectangular shape; a tracking coil disposed on the substrate; and a pair of focus coils disposed on both sides of the tracking coil in a direction of a longer side of the substrate.
The above coil substrate for a lens driving apparatus is used for a pickup of a driving unit of an optical disc or the like, and includes a tracking coil and a pair of focus coils disposed on a substantially rectangular substrate. The pair of the focus coils is disposed on the both sides of the tracking coil in the direction of the longer side of the substrate. Thereby, the length in the direction of the shorter side of the substrate can be made smaller, and the coil substrate can be reduced in size.
In a preferred feature of the above coil substrate for a lens driving apparatus, the tracking coil and the focus coils may be substantially aligned in the direction of the longer side of the substrate. In another preferred feature of the above coil substrate for a lens driving apparatus, the tracking coil and the focus coils may have a substantially equal length in a direction of a shorter side of the substrate. Thus, the length in the direction of the shorter side of the coil substrate can further be reduced.
According to another aspect of the present invention, there is provided a lens driving apparatus including: a base; a magnet fixed on the base; a lens holder supported in a state movable in a focus direction and a tracking direction in a vicinity of the magnet; and a coil substrate mounted on the lens holder, wherein the coil substrate includes: a tracking coil disposed on the substrate, and a pair of focus coils disposed on the substrate on both sides of the tracking coil in a direction of a longer side of the substrate.
In the above lens driving apparatus, a magnet is fixed on a base, and a lens holder is supported movably in the vicinity thereof. Since the coil substrate is mounted on the lens holder, by supplying the current to the coil substrate within the magnetic field generated by the magnet, the lens holder is moved in the focus direction and the tracking direction. The coil substrate includes a tracking coil and a pair of focus coils on a substantially rectangular substrate. The pair of the focus coils is disposed on the both sides of the tracking coil in the direction of the longer side of the substrate. Accordingly, the length of the coil substrate in the direction of the shorter side of the substrate can be made smaller, and hence the lens driving apparatus itself can be made smaller.
In a preferred feature of the above lens driving apparatus, the tracking coil and the focus coils may be substantially aligned in the direction of the longer side of the substrate. In another preferred feature of the above lens driving apparatus, the tracking coil and the focus coils may have a substantially equal length in a direction of a shorter side of the substrate. Thus, the length in the direction of the shorter side of the coil substrate can further be reduced.
In another feature of the lens driving apparatus, the magnet may have a plurality of magnetization boundary lines formed by an S pole area and an N pole area adjacent with each other, and the magnetization boundary lines corresponding to the focus coils may be inclined with respect to the magnetization boundary line corresponding to the tracking coil. Thus, the magnet itself can be made smaller compared to the case of having the magnetization boundary lines corresponding to the focus coils and the magnetization boundary lines corresponding to the tracking coil orthogonal with each other.
In another feature of the lens driving apparatus, the magnet may have a plurality of magnetization boundary lines formed by an S pole area and an N pole area adjacent with each other, and the coil substrate may be disposed at such a position that each of the tracking coil and the focus coils straddles the corresponding magnetization boundary lines.
In a specific embodiment, the magnet may have three magnetization boundary lines formed by an S pole area and an N pole area adjacent with each other, and the three magnetization boundary lines may coincide with three straight lines formed by connecting a midpoint of one longer side of the magnet of rectangular shape with both ends and a midpoint of the other longer side of the magnet. In another embodiment, the magnet may have three magnetization boundary lines formed by an S pole area and an N pole area adjacent with each other, and the three magnetization boundary lines may coincide with three straight lines, the three straight lines including one straight line formed by connecting a midpoint of one longer side of the magnet of rectangular shape with a midpoint of the other longer side of the magnet and two straight lines formed by connecting both ends of the one longer side of the magnet with two intermediate points on the other longer side, the two intermediate points being positioned closer to the ends of the other longer side than the midpoint of the other longer side. With those arrangements, the force for moving the lens holder in the focus direction and the tracking direction can be produced appropriately.
The lens driving apparatus according to another feature may include a pair of the magnets disposed corresponding with each other, and a pair of the coil substrates disposed facing each of the magnets. In this case, the lens holder can be moved stably according to the pair of the magnets and the coil substrate.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.